Coat-Resist Point Level Switchs

RF Admittance Point Level Switch

COAT-RESIST is a compact point level switch with integral electronics, based on RF Admittance measurement technology utilizing a three electrode design with active shield compensation. It is superior in performance to conventional capacitance based systems that often suffer from false level detection due to service material adhering to the probe electrode. It offers a satisfactory solution in tough environments where service material has a tendency to coat, where there is bridging (build up) of material between the probe electrode and side wall of the vessel, where, material particles having electrostatic charge float in the vicinity of the sense electrode, and the vessel internal temperature is high. Such environments are often encountered in electrostatic precipitators wherein no other instruments are suited. The instrument has a built in discharge device to protect it from damaging effects of static electricity.

Salient Features :

Not affected by material build up on side walls and coating on probe

Protected against frictionally induced static charge due to material movement in the vessel

High sensitivity so operates reliably in low dielectric materials like Fly ash and Plastic chips

Bar graph LED display for ease of calibration and material trend indication

Built-in Universal switched mode power supply for AC / DC operation

Field selectable Fail-safe mode for High and Low level operation

Field adjustable switching delay for probe covered and uncovered condition

Robust in construction to withstand the rigors of plant environment

High temperature versions available on request

Various mounting arrangements available to suit customer needs

Remotely mounted electronics version also available on request

Operating Principle
The probe comprises of three elements; Sense, Shield and Ground electrically insulated from each other by means of suitable insulators. The Sense element and the vessel wall (Ground) serve as the two electrodes of an electrical capacitor with the service material as the dielectric. A change in material level causes a change in the Admittance which is measured by the electronics. A Radio frequency oscillator generates the measuring frequency. An impedance transforming shield isolation amlifier is used to drive the shield actively to maintain the equipotentiality between the probe and shield electrodes thereby immunizing the probe from build up and coating. For clarity please refer to the figure on the left.